1. Field of the Invention PA1 2. Description Relative to the Prior Art
This invention relates to a method of confirming the validity of a valuable document as protection against counterfeiting, and in particular to a method utilizing a magnetic material whose magnetic properties change as a function of temperature.
The counterfeiting of currency, stocks, bonds, credit cards and other valuable documents essential to the orderly and effective carrying on of business and financial activities is a continuing serious problem. The widespread availability of high quality imaging systems and the increasing technological sophistication of the criminal combine to increase the complexity of combatting all forms of counterfeiting.
Currently, considerable resources are being devoted to the development of devices for incorporation into a document which can be detected to validate the document's authenticity. Holograms, opaque print strips and microprinting are examples of such devices, and their effectiveness depends upon the difficulties involved in counterfeiting them.
It is also known in the art to include a magnetically recordable area as an anticounterfeiting indicator on specific regions of banknotes or other valuable documents. Currently the banknote printing ink contains the black magnetic iron oxide Fe.sub.3 O.sub.4, and the presence of the magnetically detectable oxide is an indicia of genuineness. This material is readily available, and is also a major component of the toner used in many copiers. Resultantly, the effectiveness of Fe.sub.3 O.sub.4 as an anticounterfeiting measure has declined significantly as counterfeiters have become aware of its use. The anticounterfeiting method of the present invention circumvents this problem by use of materials that would be difficult for the typical counterfeiter to duplicate, and for which the sources of supply are limited. This restriction in the availability of the material is a bottleneck through which an aspiring counterfeiter must squeeze, increasing his vulnerability to detection and exposure.